Recently, the use of radio communication has become more prevalent. As a result, there is an increasing demand for communications and communication apparatuses that illustrate high performance in terms of many points such as high-speed communication, high level of reliability without disconnection of communication, and power saving in transmission device.
FIG. 33 is a functional structural diagram of a communication apparatus described in PTL 1. The communication apparatus depicted in FIG. 33 includes transmission devices 10A and 10B. The transmission device 10A includes transmitters 21-1A, 21-2A and a transmission mode switcher 22A. The transmission device 10B includes receivers 31-1B, 31-2B and a reception mode switcher 32B. In the communication apparatus of FIG. 33, the transmitter 21-1A has a function of outputting a radio signal having a frequency f1 to the receivers 31-1B and 31-2B. The transmitter 21-2A has a function of outputting a radio signal having a frequency f2 to the receivers 31-1B and 31-2B. In the communication apparatus of FIG. 33, when transmission failure occurs in a path of one of the two frequencies f1 and f2, operation of a transmitter for the frequency can be stopped and communication can be continued at the remaining frequency. For example, when transmission failure occurs at the frequency f1, communication can be continued by using the radio signal having the frequency f2 between the transmitter 21-2A and the receivers 31-1B and 31-2B. In other words, the transmission device achieves highly reliable communication without communication disconnection. In addition, in the communication apparatus of FIG. 33, when there is no transmission failure, a link aggregation function enabling high-speed communication is implemented by performing simultaneous communication at the two frequencies f1 and f2.
FIGS. 34 and 35 are functional structural diagrams of transmission devices described in PTL 2. The transmission device of FIG. 34 includes a baseband transmission signal processing unit 301, frequency converters 302 to 310, synthesizers 312 to 314, and transmission amplifiers 315 to 317. The frequency converters 302 to 304 are integrated into a single frequency conversion apparatus 321, the frequency converters 305 to 307 are integrated into a single frequency conversion apparatus 322, . . . and the frequency converters 308 to 310 are integrated into a single frequency conversion apparatus 323. The transmission device of FIG. 34 has a function of performing transmission to n pieces of sectors (transmission areas). In the transmission device of FIG. 34, a baseband signal transmitted from the baseband transmission signal processing unit 301 is converted into RF signals having frequencies f1 to fm in the frequency converters 302 to 304. The RF signals generated in the frequency converters 302 to 304 are synthesized in the synthesizer 312, then amplified in the transmission amplifier 315, and transmitted to the first sector. The frequency converters 305 to 307, the synthesizer 313, and the transmission amplifier 316 also perform the same processing for transmission to the second sector. In addition, the frequency converters 308 to 310, the synthesizer 314, and the transmission amplifier 317 also perform the same processing for transmission to the n-th sector.
FIG. 35 is a structure obtained by reforming the transmission device of FIG. 34. The transmission device of FIG. 35 is excellent in terms of a redundant structure ready for failure, as will be described below. In the transmission device of FIG. 34, frequency converters for different frequencies are aggregated into frequency conversion devices 321 to 323. In the structure of FIG. 34, there is a problem where when one of the frequency conversion devices 321 to 323 fails, communication becomes completely disconnected in the sector to which the frequency conversion device is assigned. Meanwhile, in the transmission device of FIG. 35, the frequency converters for the same frequency are aggregated into the frequency converters 102 to 104. The other constituent elements are all the same as those of FIG. 34. In the structure of FIG. 35, even when one of the frequency converters 102 to 104 is broken and communications cannot be performed at one frequency, communications in all the sectors are maintained by using another frequency. This technique also achieves highly reliable communication without communication disconnection.
FIGS. 36 and 37 are functional structural diagrams of communication apparatuses described in PTL 3. The communication apparatuses of FIGS. 36 and 37 perform transmission using two radio signals 221 and 222. The communication apparatus of FIG. 36 includes antennas 201 and 202, a duplexer unit 203, a filter unit 204, transmission amplification units 205 and 206, reception amplification units 207 and 208, frequency conversion units 209 and 210, and distribution synthesizers 211 to 215. In the communication apparatus of FIG. 36, the radio signal 221 is output from a Tx terminal of the frequency conversion unit 209 and the radio signal 222 is output from a Tx terminal of the frequency conversion unit 210, respectively. The distribution synthesizer 213 synthesizes the radio signals 221 and 222 output from the frequency conversion units 209 and 210 to generate two carrier signals and output the two carrier signals to the distribution synthesizer 212. The two carrier signals are input to both of the transmission amplification units 205 and 206 via the distribution synthesizer 212. The two carrier signals are amplified in each of the transmission amplification units 205 and 206 and then transmitted through the antenna 201 via the distribution synthesizer 211 and the duplexer unit 203. The structure of FIG. 36 is a redundant structure in which each of the transmission amplification units 205 and 206 amplifies the same two carrier signals. Such a redundant structure allows the continuous transmission of the two carrier signals even when one of the transmission amplification units 205 and 206 fails.
In the communication apparatus of FIG. 37, the distribution synthesizers 211 to 213 and the filter unit 204 are eliminated from the communication apparatus of FIG. 36 and a duplexer unit 401 is newly added. In the communication apparatus of FIG. 37, the radio signal 221 is input to the transmission amplification unit 205 from the Tx terminal of the frequency conversion unit 209. The radio signal 221 is amplified in the transmission amplification unit 205 and then transmitted through the antenna 201 via the duplexer unit 203. In addition, the radio signal 222 is input to the transmission amplification unit 206 from the Tx terminal of the frequency conversion unit 210. The radio signal 222 is amplified in the transmission amplification unit 206 and then transmitted through the antenna 202 via the duplexer unit 401. As described above, the transmission device of FIG. 37 is characterized in that each of the radio signals 221 and 222 as one carrier signal is amplified by respective individual transmission amplification units 205 and 206.
In the transmission amplification units 205 and 206, in order to suppress the occurrence of signal distortion, an average output power of the transmission amplification units 205 and 206 needs to be lower than a saturated output power (in other words, it is necessary to set a backoff amount). Suppression of the average output power of the transmission amplification units 205 and 206 at low level reduces power efficiency of the transmission amplification units 205 and 206, thus hindering power saving.
As compared to the two carrier signals (the synthesized signal of the radio signals 221 and 222) input to the transmission amplification units 205 and 206 of FIG. 36, the each one carrier signal (the individual radio signals 221 and 222) input to the transmission amplification units 205 and 206 of FIG. 37 can suppress a ratio of a signal peak power to an average power (a Peak-to-Average Power Ratio: hereinafter referred to as “PAPR”) at lower level. As a result, the communication apparatus of FIG. 37 can more suppress a backoff amount needed to suppress signal distortion, as compared to the communication apparatus of FIG. 36. Thus, the communication apparatus of FIG. 37 can achieve a higher average transmission power and a higher power efficiency than in the communication apparatus of FIG. 36. As the transmission power becomes higher, communication distance can be more extended. In addition, improvement in the power efficiency of the transmission amplification units 205 and 206 leads to power saving of the communication apparatus.